1. Field of the Invention:
This invention relates generally to control devices for position control servosystems, and more particularly relates to adaptive feedback control systems for position control of scanning micromechanical instruments.
2. Description of Related Art:
Various position control servosystems for machining devices and motor drive systems have been developed in industry. Systems for altering feed rate of tool speed to accommodate changes in volume or cross sectional area of a work piece adaptively are known; and a control system for positioning an electrical discharge machining control device utilizing an up/down digital counter for integrating servosignals for calculating a gross position error value is known. Digital speed control systems for sewing machines using a digital rate counter to determine whether to accelerate or decelerate the machine are also known. A closed loop control system for measuring and maintaining a tunnel effect variable constant in a scanning tunnelling microscope is known. Such conventional instruments integrating position signals typically utilize an analog integrating circuit to determine an actual position, an analog to digital converter for determining a digital value corresponding to the position, a logic circuit comparing present position with a commanded position, and a digital counter for determining a position error value, which can then be converted into an analog signal by a digital-to-analog converter for correction of the machine position.
In position control systems requiring extremely fast and precise position corrections, such as for positioning of scanning tunneling microscope probes, it would be desirable to provide such a highly precise and quickly responsive position control system with an adaptive feedback circuit for adjusting the rates of relative movement along the axis of movement of the position control device. It would also be desirable to utilize a circuit design eliminating an analog integrating circuit requiring the time-consuming intermediate analog to digital converter. The present invention meets these needs.